1. Field of the Invention
The present invention relates to a pull-back windup type spring drive unit used as a driving source for a toy car and others. More particularly, this invention relates to a pull-back windup type spring drive unit having two output shafts preferable for a four-wheel drive toy car.
2. Description of the Related Art
A conventional pull-back windup type spring drive unit is provided with one output shaft to which tires of a toy car are mounted at both ends thereof, and the output shaft is reversely rotated by pulling in the toy being put on a floor or the like, thereby winding up a spring. That is, the conventional pull-back windup type spring drive unit is configured in such a manner that the spring connected to a drive gear is wound up by transmitting rotation of the output shaft to the drive gear using a windup switching gear which meshes only at a time of rotation for winding and that rotation of the drive gear driven by the spring is transmitted to the output shaft by utilizing a running switching gear which meshes only at a time of rotation for running. In other words, this is a spring drive unit for two-wheel drive, which performs input and output of rotation by using a single output shaft.
Therefore, in the case where a four-wheel drive toy car is constituted by using the conventional spring drive unit, as shown in FIG. 5, the need for separately providing two units, i.e., a spring drive unit 103 for front-wheel drive and another spring drive unit 105 for rear-wheel drive involves an increase in a manufacturing cost of a toy 101. Further, since the two spring drive units 103 and 105 are aligned lengthwise when used, reduction in scale of the toy car 101 is difficult. In particular, if the units having the same winding-up and rotational directions are used, there must be additionally provided in the toy a space whose length corresponds to a length L from an output shaft 106 to an edge of the spring drive unit so as to protrude from a front wheel 102, and the scale of the toy is increased because of the thus-provided space, or the design of the toy may be restricted. Furthermore, as illustrated in FIG. 5, in the case where the spring drive units 103 and 105 are disposed in an opposed direction, it is required to prepare two units having different winding-up and rotational directions, thereby increasing the cost. Note that a reference numeral 104 denotes a rear wheel and 107 designates an output shaft on the rear wheel side in the drawing.